Google Book Search is a tool from Google that searches the full text of books that Google scans, converts to text using optical character recognition, and stores in its digital database. Many popular books are available with Google Book.
The books available can be read online only and cannot be downloaded for later use. You can download certain books as png that allows public-domain works and are free from copyright protection. Only few books are available with full preview based on agreements
with publishers.

Google Books Downloader Lite is a free, open-source utility that lets out download any book that's available in "full view" from Google Books. Of course, most of these books also feature download links right on the web page, but Google
Books Downloader lets you queue up multiple jobs and convert all of the downloaded books to PNG files.